Slotting and slitted light transmitter



Septv. ll, 1928.

Y J. KAUFMANN SLOTTING AND SLITTED LIGHT TRANSMITTER Fiied sept. s, 19252 sheets-sheet 2 @a F055 Cori/E f w mf a. 5 l 1 r/M' y n/uuh.,

lPatented Sept. 11,. 1928.

`v UNiTED STATES oFF-lcs.,

JOHN- xAUmNN, or NEW YORK, N. Y.; .assreicon To DE FOREST'rHONorILi-iconi rOnATIoN, OF NEW YORK, N. Y.,

A CORPORATION or NEW YORK.

sLoTTnaa ANnsLITTnn I LIGHT TRANSMITTER.

. Application med september s, 1925. sriai No.: 55,067.

This invention relates to improvements sIOttng, angl inslitted. lightpassages in light-transmittingmembers of sound-photograph apparatus,which apparatus may be either that for photograp ing (recording).

the sounds or the apparatus used inrepro- -ducing thev sounds, from thephotographic record-.f The sound-photograph apparatus to which-theinvention more particularly re l0 lates is that of prior inventions,wherein .the operation is by light fiuctuations,'the light rays passingthrough a slit in the l1ght-trans-- f.

mitting member of the apparatus above referred to. Usually thesound-photographing apparatus is employed in connection with'V Theobject of the Apresent invention is the. production of aminutely-slotted passage U through the light-transmitting member. of'

the sound-photograph apparatus, such slit being protected from cloggingor stoppage. by` dust, and thereby `dispensing with a dust:

Another object is thei removing air-blast. production of a light-slit ofextremely narrow width. Another object is the provision of a transparentdust-protecting cover over the light-slit, which cover shall vliesubstantially llush with the face of the -light-transmitting member,along which face theA hotographic film travels. Otherobjects w1ll`appearhereinafter.

The invention consists of the improvements Vsubstantially as described"hereinafter, specilied in the claims and shown in the drawings, ofwhich:

Figs. 1-10 are views of vthe light-trans-` li1, ihtslit,- because theslit is so narrow as to in ittinI member o r eye of the soundphotograpbut clearly illustrating the lsuccessive steps of the formation ofthepreferred extremely narrow light-slit'itself;y Y E Figs. .1l-12' aresimilar views, illustrating the manufacture ofthe product which co1nsaprises the preferably `integral combination OE- app'aratus, notaccurately to scale the. slotted light-transmittingmembe and itstransparent dust-protecting cbvergt Fig. 131s a View illustrating/-the@vassembly of the slotted and dust-protected lightetransvmittingmember-with the adjacent pants of the apparatus for recording orreproducing the sound;

Flg.' 14 is aview illustrating a modification; and l l l Figs.. 15 and ll'are views Lof other modi- 'licatlons The inventlon relatesparticularly to the art of talklng-motion pictures or phonofilms.Heretofore in this art, the light for' the sound-photography andsound-reproduction has been. supplied to the photographic near one edgethereof (Fig.- 13) through a` slotted member or eye across'i'the frontof which the film is moved intermittently. The slits 1n this eye havebeen oblong, short and narrowopemngs about 1/16 to 3/32 inch long by am11 and half wide.` It is highly desirable, for optical reasons, thatthese narrow slits be made even narrower, but even the onc-mil slitsheretofore used have been liable to clogging by dust carried by themoving photograph film,which liability obviously wouldbe furtherincreased by reducing the width of the light-slit. An air-blast has beenused, directed through the light passage, to keep it free of dust, ybutthe photo- ,graphie film for best results should travel through a fixedplane at constant distance from the front face of the light-transmittingmember and -in front of the light-slit, and such air-blast has blown thefilm so that, in addition to its desired movements across the face ofthelight-transmitter, its distance therefromhas been varied undesirably.causing more or less indistinctness of image of light on the film,resulting in faulty regis-4 tration for recording and in unfaithfulreproduction of sound. Furthermore, the film, 'for best results, shouldtravel as close'as possible to the face of the light film, thisfactheretofore having militated against 'the'pro vision of a.dust-protecting cover 'for the make it -impraeticable to insert adust-proteotorbetween'the inside walls ofthe slit, and` anydust-protector should not project substantially beyond the front face ofthe light-transmitting member vso as to prevent the proper 'positionofthe film close to the light film.

In accordance with the present invention, the slit is made of thedesired extremely minute width of half a mil, or even a smaller fractionof a mil; it is adequately protected against entrance of dust brought toits vicinity by the moving photographic film; and the construction isof. such nature that the film can travel uniformly close to the frontface of the light-transmitting member, the dust-protecting cover beingsubstantially iiush with such face although not'located between theinside walls of the extremely narrow slit itself.

The slit is formed, by a series of manufacturing operations, in a metalblock or plate M (Fig. 1), the front end of the resulting slit beingshown at S in Fig. 8.

Thereupon a transparent cover TC (Fig.

' 12) is united with light-transmitting member M, the construction beingsuch thatvthe projecting thickness of cover TC is so slight that" thefront face of the cover is substantially fiush with the face of member Mitself in the sense that the film PF (Fig. 13) can travel close to theface of member M, although this cannot be indicated in the assembly ofFig. 13 on account of the slight thickness of cover TC. In fact, thedimen sions of slit S, Fig. 10, and of cover TC,

Fig. 13, and in the other drawings, are

necessarily greatly enlarged for elearness.

The manufacture of the eye member which results in the formation of thespecific slit S of Fig. 10 will be described in connection with Figs.1-10.

consists of material which preferably is tough (non-brittle) andductile, in order to permit the successful execution of themanufacturing steps to be described. The material of member M may be,and preferably is, copper, but it may consist of other materials havingsaid desired properties, such as other metals, or alloys of metals, ormaterial which is non-metallic or comprises a nou-metal element.

1st. (Figs. 1-2). A circular depression A, preferably tapered as shown,is bored or drilled in the back of member M(i. e., Fi 13, its faceremote from the traveling films?. Fig. 1 shows the back of member M..De-

pression A may be about 5/432 inch in diameter at its entrance andpreferably 3/32 inch at its bottom B, the taper extending from theentrance to said flat bottom. The diameter at the entrance of hole A isrelatively immaterial, butthe hole is preferably tapered in order toermit free access to the instruments emp oyed in the further operationsto be described. The diameter of Hat bottom B corresponds with thelength of slit S, Fig. 8, which is the final object of these operations.The dimension as long as 3/32 inch (for the diameter of flat bottom Band for the length of slit S) is preferred herein on account of theextreme desirable narrowness of the slit (half a mil, or'evcn less) inorder to provide for sufficient illumination.,

Fig. 2 is al central section of Fig. 1, diametrically of depression A,showing flat bottom B, and the comparatively thin rcniaining undrilledportion or wall Z, the thickness Z of co per plate M being as thin ascan be obtainef conveniently bv the drilling or boring tool, say,about 3mils, more or less, but the thinner the better within the practicallimits of the boring operation.

2nd. (Fig. 3, lookin into depression'A and upon Hat bottom di). A secondand smaller V-shaped depression or trough (V, Fig. 4), having a centralbottom or ridge R (Fig. 3) is Formed in fiat bottom B across thediameter thereof. This is done by means of a small chisel or punchingtool' the copper downwardly, Fig.y 4, forming a wale W on the front faceof member M. The surface of fiat bottom B is depressed at the trough V,as shown in Fi 4. which is a section of Fig. 3, as indicate The metalformerly occupyingsuch space V is driven downwardly toward the frontface of member The metal formerlyoccu ying the space at the surface' ofmember 1s driven by the sharp punch or4 chisel downwardly beyond saidsurface so as to raise the wale W into more or less of a V-shape, Fig.5, in conformity with inside V-shape of trough V, Fin. 4.

Up to this oint, the. thickness of this bottom wall Z, IFig. 4, has notbeen changed materially, the principal change being the change from thefiat circular bottom wall B of Fig. 1 to the condition shown in Figs. 3and 4, where the bottom B yet is flat save along the trough or indent Vformed by the chisel. The object and the result of this operation is toform Wale W, Figs. 4, 5, projecting slightly beyond the face of thinmember M, from the much thinner wall Z- and along the length of thedesired slit S, Fig. 8; so that as a result of the formation of Wale W;the wall Z may be reduced,

to a yet thinner wall or lm of metal preparatory to the ultimaterforation of such film to fgrm the slit While Wale W,

llu

Fig. of course is not muchof` an elevation above the face of member M,yet it is sutilandxwale W (outside), yet, since the func- .cient `to bevisible,`at thissgxe, to the uns ile the edge' .ofthe chisel o'rothersharp punch is suf-f aided eye of the artisan.

ciently sharp to produce trough V (inside) tionl of this chisel-cut islnot to form a slot throughbottom B, thechisel is not so thin as theinstrument later to be used to slot v thel thinv bottom `ofdepression Ato form I all the-operations leading up to and includthey slottingare'very delicate and require v. the utmost of combined manipulatoryand` ocularartisanshi and even so the work is liable to be ruine i-'nprocess. Butthe" A desirability of the object is so great, the

vthat temporary improvement so valuable in respect of the i,

sound photograph and reproduction art,

ai uresare discountable because quite satisfactory products have beenmadeby themanufacture herein described., `3rd. The wale W of, Fig. 5.then is ground yor planed down until, as shown in Fig. 6,

it has; disappeared `from the face of plate -.M,. said face. remainingportionof wall'Z of. Fig. 4 being, @Ffig. 6, a thin integral ihn F alongthe vlength'ogl the rid e or bottom R of trough is thinnest along a linel ,runningwith said ridge R, where it pref 4 V, Fig. 3.-A Film eingentirely flat, and the only c erabl is and can bev made, by theprocessdescribed, to lbe less than Vone mil thick or evenless. The section ofFig. 7 is ta en degrees vto Fig. .6, as indicated, Fig. 7 Y beinganattemptto .indicate a-section of the width of lilm F, which actually'islittle more than a line of' metal iilm at rits l,portionl along thelength of ultimate almost mioroscoplc slot S of Fig. 8. Fig. ,7,xhowever, also 'in diCatesthe fact that inthe original region indicatedat X, (on opposite sides of` lultimatefslit S), the metalwall at thebottom. of depression A now is very 1thin 'although thicker 'thanline-'film F,.being of gradually decreasing thickness from the topsofthe sides A of trou h V down toward ridge R of trough V. lene, sincethe wall thickness Z of Fig. 4, including wale W, was onlyabout 2 or 3mils, and since wale i W now has' been eliminated, and since lilm l F atridge R of trough Vhas been formed with a thickness of about a mil or'even half f 'a mik-the wall thickness X, Fig. 7, will vary 'betweenhalf a mil-u to 2 or 3' mils, and in 4the immediate vicimty 'ofline-film F the wall thickness onboth sides of 4 said lm will lill . areve mil, such. thickness extending M to which thin glass cover TC ofFigs.

n'11--12 later (after formation of slit S) is 'f united by fusion, andthe thickness of this wall X may have something to do in facilitatingsuch fusing operation.

4th. Thin, narrow, integral metal film F 70 next is slotted (Fig. 8) 'toproduce light-slitI S of Figs. 8-10. This is done by a chisel or shim'having a thinner or sharperedge than that of the chisel or punchemployed in forming the trough V of'Figs. 3-7, said 75 first chisel orunch being relatively blunt. l Thisslotting shim or chisel for theslotting t operation of Fig. 8 is of hardened steel ground` to .a thincutting edge of substan- Atial depth and of a thicknesslwhich" is ex- S0,l

actly that ofthe desiredwidth of the slit S, i. e.` halfa mil or even asmaller fraction of a mil. This slotting shim is inserted down throughdepression A and trough V,

'Fig. 8,' the v'vallrofatrough V guiding the S5 'slotting instrumentdown toward line-film F (Fig. 7). Then the'slotting tool is tappedlightly to cause its edge to perforate film F, producing slit S of thedesired length (of the width of thecutting edge 'of the 9".

tool) and of a width corresponding with the length of the edge of theslotting tool; Saifdslit S'fornii'ng alight passage through an1 integralfnrietal wall (F) which is only about half .aI'nil or a mil thick, at'the botv toni-of trough Through slit S light-rays passA via relativelyllarge tapered circular Y bored depression A, and via trough V. l TheYdepth of thethin cutting edge of the slotting tool is relativelysubstantial and suiiicient if", to prevent'undesiredenlargement of slitS. after the front edgeof -the tool has perfo-v rated film F; but suchdepth of lthe cutting edge actually is not ver great, preferably beingless than the dept of the trough V m5 in Fig. 7 .after the eliminationof Wale of Figs 4-5; so thatthe part of the slotting tool above itscutting edge may be shaped like that of the relatively blunt-edged punch'or chisel used to form trough V, and so that @1m the -slotting tool maybeguided to its slotting` operation. Thus, the sharpened slotting toolor shim, before its cuttin edge reaches Elm F, will be guided by theside walls of trough V so as lto aline the cutting edge with narrow thinfilm F. Y

By this method itis practical to make slit S asA narrow as half amil oreven less. Fig. 9is a section like Figs 4 and 6 showing theIengthotrGugh V; but Fig. 9 also shows 120 slit S in elevation asextending through the bottom of trough VV. The ductility or lack ofbrittleness of material of member M pre v ventsbreakage along lineswhich would `,con- Y stitute substantial departures from the de-` .|25

ar channel S through although,of course, `minute sired rectan vB of latepartie es' of metal may`remainas lips around the ed es of slit S.

5th. ext, by means of an oil-"stone, the 130 I front face of plateMaround slit S is polished smooth and planed, (Figs. 9-10) removing anyslight lips of metal which may remain after the slottinc operation ofFig. 8. Slit S as formed hereby is so narrow that after this operationit is almost invisible when the front face of member M is viewed inreflected light, and becomes clearly visible to the unaided normal eyeof the observer only when member M is held so that slit S is in linebetween ones eye and a source of light.

6th. Plate M next is provided with a transparent cover TC over slit S11-12). applied on the portions ofthe front face .of M which surroundthe slit; and this application is made so as to provide a cover whichshall besubstantially flush with the front face of member M, i. e.,which shall not project sufficiently beyond said front face to preventthe photographic film (PF, Fig. 13) from traveling very close indeed tosaid front face, as is essential for best soundphotography. It would bedesirable to mount a transparent window pane inside slit S between theWalls thereof, but the extreme narrowness of the slit makes thatimpracticable. A very thin, flat, smooth sheet of clear glass or quartzTC of any desirable superficial configuration Iis laid (Fig. 11) on topof member M so as to cover slit- Sand also a substantial portion of wallX (Fig.-7)` of member M around the slit; so that there will besubstantial surface contact between cover TC and the thin integral wallX, Fig. 7 ,'of member M.

While this transparent cover TC, at this stage, (Fig. 11) may be asthick as one mil,

more or less (preferably in connection with the form of member M thusfar disclosed), requiring later treatment to reduce its thickness sothat it lies substantially flush with the front face of member M', andwhile at this lstage (Fig. 11) the transparent cover TC may be too thickfor the final product, yet theim ortant object 'of the present oper.-ationl of fig. 11 is permanently and integrally to unite cover TC withmember M; and this may be done with an initial thickness of TC as greatas one` mil. The cover TC, however, is, at this stage, as thin" as isconvenient to handle and a thickness of 'one mil is satisfactory, beingthin enough to permit the fusing operation now to be described. Thethickness of metal wall X, Fig. 7, with which cover TC makes contact,has been above described as being very slight, altho a little greaterthan the depths of slit S. Cover TC preferably extends only slightly,beyond the edges of slit S, which, as described,`is only a fraction ofa mil wide and 1/16 to 3/32 of an inch long; so that the superficialdimensions of cover TC. need not be very large, notwithstandin that itexas to be united with this wall X member M (Fig. 7). Under theseconditions the parts M and TC are subjected to a high temperature ofabout that of the red heat of iron, which is the fusing point of theglass. (If quartz be used, it is cemented to member M.)

This fusing operation can be conducted with a gas flame, but preferablyis effected in a suitable furnace, .as one heated by a gas flame. 1

In order to avoid destruction of the cover TC by the fusing temperature,lit is desirable to raise the temperature of member M gradually, so thatthe portion of its surface l(Wal X) adjacent glass TC will not delay theheating of the adjacent surface of the glass.

wall X, Fig. 7, to the outer surface of which cover TC is fused,contributes to the suflicient fusing of the adjacent glass surface priorto injurious action of the high temperature on the glass cover TC as awhole.

Under the above conditions, the contacting glass surface of TC Vwill befused tothe adjacentv copper surface lof wall X (Fig. 7), so that partsM and'TC will 'be united by such fusion, the material of transparentcover' TC beingl in absolutel close chemical cohesion with thecopper ometal wall X, Fig. 7, justas if both these parts were of metal andwelded together. 'Promptly upon this integral joining by fusion, theapplication of the high' temperature is discontinued,-so as to avoidinjury to the thin cover TC, but thereafter the cooling should not besudden but preferably should'be as slow as possible. Whereupon thedparts M and TC will be permanently unite in (Fig. 12,) In effect thisprodgral structure arent film or coating uct is a thin trans adherent tothin wa slit S.

7th. Small, thin, transparent lcover now, by' virtue of itsincorporation in member M, is in condition which will ermit convenientreduction of its thickn ss. .As is sought to be indicated in Figs. 12and 13, it is thicker in the former figure than in the latter. VAfterthe fusing operation, there- 'fore, the surface of cover TC is grounddown (as by a .grindstoe) frolfi the thicknessiindicated in Fig. 12. Itsouter surface then is polished (as by a whetstone) until the glassorquartz is perfectly clear and the' thickness TCis reduced to afraction, and preferably a small fraction, of a mil, as indicated butnot practicable to be actually shown in Fig.`13.

8th. Member M, with its slit S, preferably of a small fraction of a mil,and protected by the integral'transparent cover TC of a like' order ofthickness and located .substantially flush with the front face 'ofmember M, now is assembled with plate P of Fig. 13

X of member M over,

It is probable thatthe thinness of' l a single intelll) tends sufcientlybeyond the e ges of slit S in the camera or projecting-machine, plate13" l P being the art acrdssV which the photographic lm F'travelserpendicularly to the plane of the sheets ofJdravvings).l Fig. '13 showsmember M and its' united cover TC, in elevation and mounted in place vinplate P, shown in section. As shown in F ig.'A

13, transparent cover TC, over light-slit S in member M, isvlocated soas to bein lightcommunication with the righthand side of photographicfilm PF near onev longitudinal edge thereof, on lwhich the sound is tobe or has been recorded, the photographs of mo- .tion being, as usual,onthe central portion of film PF to the leftL of cover TG and the. extremesides of film PF next its longitudinal edges being perforated, asordinarily, to permit the mechanism of the camera 'orVprojecting-machine to move the film transversely to the len'gth of slitS. Although in FigQlS the transparent cover TC is shown as projectingsubstantially beyond the front -face of member4 M, yet actually, inaccordance with the above description, coverTC lies substantially iiushwith such face,it being impossible in the drawing to show this of theslit, yet inthe modification of Fig. A14

the cover is prevented from projecting even -a fraction of a milbeyoridthe front face of the member M by being inset in the fiat-bottomeddepression-D bored in the front face f of memberM early in. theoperations, as

about the time when depression A, Figs. 1, 2, is bored ;l themanufacture otherwise being permissibly the same .as Figs. 1-12, if deasired, or Figs. 1-10. The diameter of depression D of Fig. 14 isimmaterial, save.

that it should be suiiicient to permit convenience of conducting theoperations of Figs. 2-10, in cases where those arel executed on themodification of Fig. le as is preferredi In this modification, cover TGmay be of any desired thickness up to the maximum permitting'securing tomember M by fusion;

ut'th'e walls of depression D lmay serve as supports for the cover TCand the latter be secured thereto in proper position in depression D byany suitable means other than fusion, and including cement (as in thecase 'of a TC ,of quartz); and in such case the cover TC may be of anydesired dimension of thinness. or thickness, unlimited by anyrequirement of fusion and permissible by optical conditions and by thematerial of which the cover TC itself may be composed.

former. Here (Fig. 13)

, The. advantage of any modification `including depression D- of Fi 14in connection with the operations o-Figs. 1.-10, is that it obviatesthereduction in thickness of cover TC by the grinding vand polishing(Fig. 13) after fusing (Fig. 11). Whatever the .thickness of coverTG1-may be, the depth of depression D is preferably substantially thesame as that, so that the front face of the cover will lie absolutelyflush withy the front face .of member M after the cover is suitablysecured within the depression.

Fig. 15 illustrates` another modification,l

wherein the desired substantially plane surface yfor presentation tophotographic film PF, Fig. 13, is provided, (in lieu of the method (ofFi s. 11v-12, and in lieu of depression "D o Fig. 14), by a transparentcovering PFC, wh1ch extends over all or as much of the-plane frontface'of member M as is desirable, in order to present a plane surface tothe photographic film (Fig. 13") and Apermit the latter to `travelcloseA to the covering PFCmay consist of a sheet ofthe base materialemployed in photographic and to which the sensitive chemical coatingthereof is applied 4in producing photographie sensitivityjand such basefilm readily can be cemented at T to the face of member M. Other formsof transparent the transparentcovering (-notably'of' very thin mica)mayA be applied in this manner, i. e., by cementing them to a largeextent of the face of member M, and in these cases slit S may be formed'--in any desired manner, although preferably as in Figs. 1-10. V1

Although, on account' of the preferably minutely narrow width of slit S,it is 11npracticable to locate in dust-sealing relation in side thewalls of the slit any previously-shaped transparent soliddust-protecting cover or shield, yet in Fig. 16 is illustrated a methodby which a shield of glass or the like may be mounted inside the lightAchannels which extends through the thin wall X, Fig. 7, of member M. Inthis case the metal member-M itself, fabricated as in Figs. 1-104 butnow not previously heated, has applied to it, over slit S, a minutemolten mass MG of a material such as glass cement or glass (see below),which is sohdat ordinary temperatures or upon drylng;4 and thereupon thesmall soft 4fluid or molten mass is pressed toward member M, causin avery small 'portion indeed of mass M to be forced into slit S betweenthe walls thereof, or to extend across the end ofthe light channel so asto avoid formation ,of a prism 'which would absorb too much light ordiffuse it too much.

Thereupon the entire mass vof fluid molten materialMGis allowed tocooland solidify, and'. the excess beyond a slight thickness outside-ofslit Sfis ground completely ofi',

l leaving onlylr a minute amount inside the slit or`at its opening indust-sealing relation to the walls thereof and flush with the surface ofmember M.- The mass MG ma consist of transparent liquid chemp icacombinations not requiring to be fused,

such as p oxylin, collodion and the lilre, including t osehaving analcohol constituent or solvent, so that the solvent will evaporate,

leaving a transparent solid residue inside slit S and sealin it. In suchcases, the liquid maybe app 'ed on to of member M over a large ortion ofthe ont face thereof and over s 't S, and forced into or merely over theslit .(or both bymeans of application with a brush an then allowed tosolidify by evaporation of the solvent. Slit S is so narrow that 'itssurrounding metal wall will support various kinds of such coatings,

including a transparent coating of shellacf vThe advantages 'of theinvention above .specifically described are in. eneral that it providesa desirably narrow Ig1ghtslit,'which is,` prevented from becomingvclogged with dust by means of a transparent coating or cover, whichmakes unnecessary any air blast, but which will, by being substantiallyflush with the light-transmitting member,

permit the front face thereof to be traversedby the photographic lilm inclose relation 'thereto and always in the same plane.

In-an case', tlie greater part of themass of mem r M constitutes asupport and protection for the integral film (Figs. 6-7),

part of which is perforated to-form dslit S and such grosser mass servesto su port sai slotted film F in proper position in plate P of Fig. 13,relative to the o eration of the fphotographic fili PF on w 'ch thesound photographs have been 6r are to be made. 1

In the claims, the words glass and metal are used inclusively ofequivalents;

" and the expression sound photograph apparecording a paratus.

' than'a mi in thickness, said -lilm being pery.

. with a portion consisting of a thin integral` ratus is-intended toinclude the sound. re- -producing apparatus, as well as the sound l. Ipartie arlyppomtV out and' distinctly claim the art, improvement orcombinationwhich vI c aim as 'my as follows 1. A light-tra 'ttingelement .for a. light-fluctuating sound-photograph a tus, comprisingacopper mem r ormed with a portion. consisting of a thinselfsupportinintegral film substantially less invention or discovery forated in theform of an oblong slit having a width of a fraction of'a mil." l

A 2. A light-transmitting. element for af light-ductuatingsound-photogra h a paratus, comprising a co per mein er ormed lm, saidilm be' perforated` iii", the form ,of an oblon slit having a width of afraction of a mil; and a thin transparent dustmember in -linewith saiparaexcluding coating adherent to said i copper member and extendingover .said slit as a dust protector.

3. A light-transmittin element for a light-fluctuating sound-p otographappara.u

.a glass cover extending over said slit as a dust protector and 'fusedto the' surface of said copper member around` said slit. v 5. Aight-transmittin b light-iuctuating sound-p otograph apparatus, whichcomprises a member formed with a light-'slithaiglng a width of the orderof a fraction of a and having fused to it ai transparent cover extendingover .the

element 'for a slit; the outer face ofsaid slit-cover beingsubstantially Hush with 4the face of thc slotted member.

' 6. A light-transmittin light-fluctuating soundotograph ap aratus,which comprises a metal member ormed with a relatively long narrowslit;. and

a 'cover of transparent material extendin .over said slit, fused'to theface of the meta element vfor av member around the slit, and having athick-f i ness of the order of a mil or less.

.7. A li ht-transmitting "element for a light-fluctuating soundhoto aphapparatus, comprising a mem er ormed with a `depression having a flatbottom, and formed withv a trough extending across the at bottom, andformed also witha thin integral film on opposite sides of the ridge ofsaid trough; Vsaid film being .perforated along the rid e of the troughto constitute a constricte light-channel having a correspondingly narrowentrance-slit.'

8.A A .light-transmitting, element for a light-fluctuating soundhotograph apirag tus, comprising a mem r formed wiinwardly-taperedfdepression and an integral wall closing'the'"bottomofi; ,il de ression save v:for a pprfggaton of' sai Il, formof an olongiiarrow slot; and 'a'trans- Iparent dust-excluding coverrsecured tosaid ,l member and extending. over said slot, the l* wholef presenting asu stanti'all'y', plane surface to the hotograph film. i

i). A lig ttransmittin light-fluctuating sound-p otogra h'a 'paras tus,which'comprises a metal me er ormed with a depression ofcomparativelylarge wa inthe 'element 'for a' A diameter extending almost through it;and

land integral film -separatin said depression ong narrow slit.

10. A blank for a light-transmitting. element for a light-fluctuatingsound-photol graph apparatus, said blank comprising .a

moving the projecting portion of the member formed with a depression ofcomparatively large diameter extending almost through it7 and anintegralfilm having a portionless than a mil in thickness separating thebottom of said rclepressionfrom the opposite face of said member.

11. The improvement in the manufacture of a light-transmitting elementfor a lightfluctuating sound-photograph apparatus, which consists informing a. portion of a tough ductile member into the form of anintegral film having a portion less than a mil in thickness, andthenperfor-ating said fil'm to form a minute light-passage in the form of anoblong narrow light-slit.

12. The improvement in the manufacture of a light-transmitting elementfor a lightfluctuating sound-photograph apparatus, which consists informing a portion of a tough ductile member into a part havingcomparatively sli ht thickness; punching an oblong portion o said thinpart slightly beyond the facev of 4said duct'ile member; re-

thickness, l said lm being perforated "to form anoblong narrowlight-slit.

14. A light-transmitting element for a light-fiuc'tuatingsound-photograph apparatus,ywhich comprises ametal'light-transmitting-member having a portion in the form of anintegral lm less than a mil in thickness, said film being perforatedforming an oblong light-slit of extremely slight Width.

15. A light-transmitting element for a light-fluctuating sound-photograh a paratus, which comprises a metal mem er ormed with a portion ofreduced thickness and with a light-channel extending through it andterminating at said thin portion of the metal member at a surfacethereof, said thin portion being formed with a fine slitl smaller thanthe rest of the light-channel and constituting a continuation and thetermination of said light-channel; and a thin transparent member locatedsubstantially at said surface of said metal member and extendin acrosssaid slit in the thin portion thereo JOHN KAUFMANN.

